ADHD and Parkinson’s disease

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The chemical dopamine plays a critical role in Parkinson’s disease.

It is also involved with the condition Attention deficit hyperactivity disorder, and recently researchers have been looking at whether there are any links between the two.

In today’s post we will look at what Attention deficit hyperactivity disorder is, how it relates to Parkinson’s disease, and what new research means for the community.


o-ADHD-facebook

Source: Huffington Post

We really have little idea about how Parkinson’s disease actually develops.

It could be kicked off by a virus or environmental factors or genetics…or perhaps a combination of these. We really don’t know, and it could vary from person to person.

There is a lot of speculation, however, as to what additional conditions could make one susceptible to Parkinson’s disease, even those conditions with early developmental onsets, such as autism (which we have previously written about – click here to see that post).

Recently researchers in Germany have asked if there is any connections between Parkinson’s and ADHD?

What is ADHD?

Attention deficit hyperactivity disorder (ADHD) is a neurodevelopmental condition that begins in childhood and persists into adulthood in 60% of affected individuals.

It is classically characterised in the media by hyperactive children who struggle to concentrate and stay focused on what they are doing. They are often treated with drugs such as Methylphenidate (also known as ritalin). Methylphenidate acts by blocking a protein called the dopamine transporter, which is involved with reabsorbing the chemical dopamine back into the cell after it has performed it’s function.

1280px-Ritalin

Ritalin. Source: Wikipedia

So are there any connections between ADHD and Parkinson’s disease?

This is an interesting question.

While there have been no reported findings of increased (or decreased) frequency of Parkinson’s disease in people with ADHD (to our knowledge), there are actually several bits of evidence suggesting a connection between the two conditions, such as abnormalities in the substantia nigra:

substantia

Title: Structural abnormality of the substantia nigra in children with attention-deficit hyperactivity disorder
Authors: Romanos M, Weise D, Schliesser M, Schecklmann M, Löffler J, Warnke A, Gerlach M, Classen J, Mehler-Wex C.
Journal: J Psychiatry Neurosci. 2010 Jan;35(1):55-8.
PMID: 20040247               (This article is OPEN ACCESS if you would like to read it)

The substantia nigra is a structure in the brain where the dopamine neurons reside. In Parkinson’s disease, the dopamine neurons of the substantia nigra start to degenerate – 50% are lost by the time a person is diagnosed with the condition.

In this study, the researchers used a technique called echogenicity to examine the substantia nigra of 22 children with ADHD and 22 healthy controls. Echogenicity is the ‘ability to bounce an echo’. This sort of assessment measures the return of an ultrasound signal that is aimed at a structure.

The researchers found that the ADHD subjects had a larger substantia nigra area than the healthy controls – which apparently indicates dopamine dysfunction. This finding is similar to results that have been observed in Parkinson’s disease (Click here to read more regarding that study).


Another connection between the two conditions was recent research has shown that genetic variations in the PARK2 gene (also known as Parkin) contribute to the genetic susceptibility to ADHD.

Parkin title

Title: Genome-wide analysis of rare copy number variations reveals PARK2 as a candidate gene for attention-deficit/hyperactivity disorder.
Authors: Jarick I, Volckmar AL, Pütter C, Pechlivanis S, Nguyen TT, Dauvermann MR, Beck S, Albayrak Ö, Scherag S, Gilsbach S, Cichon S, Hoffmann P, Degenhardt F, Nöthen MM, Schreiber S, Wichmann HE, Jöckel KH, Heinrich J, Tiesler CM, Faraone SV, Walitza S, Sinzig J, Freitag C, Meyer J, Herpertz-Dahlmann B, Lehmkuhl G, Renner TJ, Warnke A, Romanos M, Lesch KP, Reif A, Schimmelmann BG, Hebebrand J, Scherag A, Hinney A.
Journal: Mol Psychiatry. 2014 Jan;19(1):115-21.
PMID: 23164820         (This article is OPEN ACCESS if you would like to read it)

There are about 20 genes that have been associated with Parkinson’s disease, and they are referred to as the PARK genes. Approximately 10-20% of people with Parkinson’s disease have a genetic variation in one or more of these PARK genes (we have discussed these before – click here to read that post). PARK2 is a gene called Parkin. Mutations in Parkin can result in an early-onset form of Parkinson’s disease. The Parkin gene produces a protein which plays an important role in removing old or sick mitochondria (we discussed this in our previous post – click here to read that post).

In this report, the researchers conducted a genetic sequencing study on 489 young subjects with ADHD (average age 11 years old) and 1285 control individuals. They replicated the study with a similar sized population of people affected by ADHD and control subjects, and in both studies they found that certain deletions and replications in the Parkin gene influences susceptibility to ADHD – two of the genetic variations were found in 335 of the ADHD cases and none in 2026 healthy controls (from both sets of studies).

So there are are some interesting possible connections between  ADHD and Parkinson’s disease.

And what has the recent research from the German scientists found?

In this study, the researchers have looked at additional genetic variations that have been suggested to infer susceptibility to ADHD.

adhd

Title: No genetic association between attention-deficit/hyperactivity disorder (ADHD) and Parkinson’s disease in nine ADHD candidate SNPs
Authors: Geissler JM; International Parkinson Disease Genomics Consortium members., Romanos M, Gerlach M, Berg D, Schulte C.
Journal: Atten Defic Hyperact Disord. 2017 Feb 7. doi: 10.1007/s12402-017-0219-8. [Epub ahead of print]
PMID: 28176268

The researchers analysed nine genetic variations in seven genes:

  • one variant in the gene synaptosomal-associated protein, 25kDa1 (SNAP25)
  • one variant in the gene dopamine transporter (DAT; also known as SLC6A3)
  • one variant in the gene dopamine receptor D4 (DRD4)
  • one variant in the gene serotonin receptor 1B (HTR1B)
  • three mutations in cadherin 13 (CDH13)
  • one mutation located within the gene tryptophan hydroxylase 2 (TPH2)
  • one mutation located within the gene noradrenaline transporter (SLC6A2)

These genetic variations were assessed in 5333 cases of Parkinson’s disease and 12,019 healthy controls. The researchers found no association between any of the genetic variants and Parkinson’s disease. This finding lead the investigators to conclude that these genetic alterations associated with ADHD do not play a substantial role in increasing the risk of developing Parkinson’s disease.

Have ADHD medications ever been tested in Parkinson’s disease?

Yes.

Given the association of both ADHD and Parkinson’s disease with altered dopamine processing in the brain, a clinical trial of ritalin in Parkinson’s disease was set up and run in 2006 (Click here to read more about that trial). The results of the trial were published in 2007:

 

Ritalin title

Title: Effects of methylphenidate on response to oral levodopa: a double-blind clinical trial.
Authors: Nutt JG, Carter JH, Carlson NE.
Journal: Arch Neurol. 2007 Mar;64(3):319-23.
PMID: 17353373       (This article is OPEN ACCESS if you would like to read it)

In this study, the researchers recruited 12 people with Parkinson’s disease and examined their response to 0.4 mg/kg of ritalin – given 3 times per day – in conjunction with their normal anti-Parkinsonian medication (L-dopa). They then tested the subjects with either ritalin or a placebo control and failed to find any clinically significant augmentation of L-dopa treatment from the co-administration of ritalin.

What does it all mean?

So summing up: both Attention deficit hyperactivity disorder (ADHD) and Parkinson’s disease are associated with changes in the processing of the brain chemical dopamine. There are loose connections between the two conditions, but nothing definitive.

It will be interesting to follow up some of the individuals affected by ADHD, to determine if they ultimately go on to develop Parkinson’s (particularly those with Parkin mutations/genetic variants). But until then, the connection between these two conditions is speculative at best.


The banner for today’s post was sourced from Youtube

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5 comments

  1. Mijoon Pak

    Finally, some articles for laymen linking these two conditions! I am a 38-year old female who was recently diagnosed with ADHD (which I suspect I inherited from my mom). My mom is showing some early possible signs of Parkinson’s disease now and I am worried (and I believe my mom is terrified) because her mother–my grandmother– suffered from Parkinson’s for almost 20 years before she passed away. after doing some research I suspected a possible link between ADHD and PD and brought this up to my doctor but he dismissed this idea. I found some schoarly article about a link but it seemed there is a long way to go to truly shed some light on how these two are linked. Thank you for this posting and the list of studies and summary. Greatly comforting. Hope more is found out soon.

    Like

  2. Lawrence

    Why does a clinical researcher look to a chemical solution and not a behavioral treatment. Gee it sure would be great it a little medication could cure ADHD and Parkinson’s Disease. It could also be very profitable to the pharma industry. What research has proven is that brain chemistry and structure in the PD patient is different for each patient. I have found that using a high intensity exercise routine 3 days a week have had significant positive results for my PD. I have not found that the attention disorder is a chronic behavioral issue that can be addressed best by following the directions of a “coach”. Unlike PD which is significantly mitigated by levo-dopa medications, the ADHD meds are not able to cure the typical symptoms of ADHD. However if taken in conjunction with a treatment plan of organizational behavioral therapy and long term conditioning, the ADHD can be mitigated. I haven’t heard of a clinical study for PD patients with ADHD. If anyone knows of such a trial or knows of a treatment for these combination of conditions please post.

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  3. Simon

    Hi Mijoon, Thanks for your message – sorry for taking sooo long to respond to it (not sure how we missed it!). Sorry to hear about your mum, has she seen anyone about it? We would be interested to know what other ‘scholarly articles’ you found regarding the possible connection between these two conditions. It is a very under researched area, and worthy of further investigation.
    Glad you liked the post.
    Kind regards,
    Simon

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    • Mijoon

      Thank you for your kind regards. My mom is decided against seeing a doctor for now, thinking the disruption of her routines and peace of mind outweigh the benefits. I hope I will be able to persuade her to get the help she need soon. With regard to the articles I have found, here are some.
      (1) https://www.ncbi.nlm.nih.gov/pubmed/24911152
      This paper reports of various scanning, experiments and treatments of a single patient, particularly on two mutations he has in dopamine transporters, one of which the researchers say linked to parkinsonism for the first time. What was interesting to me was how methylphenidate treatment for the patient produced “unacceptable side effects” and how the patient did not feel alleviation of his symptoms. This sounds rather like my own case, and I wonder if what is called ADHD is actually a set of slightly different disorders that should be treated with different drugs, and if one or more of them is more closely related to PD than the others.
      (2)
      https://www.ncbi.nlm.nih.gov/pubmed/17982908
      https://www.ncbi.nlm.nih.gov/pubmed/22470460
      These two studies combined made me think twice about what disorder I have and what drug I should take. They suggest that methylphenidate treatment could produce “neurodegenerative consequences and “may be a risk factor for the development of Parkinson’s disease”.
      (3)
      https://www.ncbi.nlm.nih.gov/pubmed/17197367
      This study describes a loose connection between ADHD, PD and schizophrenia. One of my aunts (my mom’s elder sister) has had schizophrenia for almost 50 years, which I heard was triggered by domestic violence of her husband. I also heard that my grandmother was electrified while changing a bulb shortly before she exhibited first PD symptoms. None of her siblings are either alive or diagnosed with one yet, although my mom has stiff joints (comes and goes), slow walk as well as impairment of fine manual control. She can no longer peel apples and her handwriting is bigger and shaky than it was before.

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  4. Simon

    Hi Lawrence, thanks for your message.
    “Why does a clinical researcher look to a chemical solution?” – I think it’s a case of a man with a hammer looks at every problem as a nail. All joking aside, I actually started out in behavioural psychology and still believe strongly in many of the laws of behavioural conditioning. I completely agree with you that a combination of treatment regimes is the best approach to PD and ADHD.
    Regarding exercise: something sadly missing on this website is a few post regarding physical exercise, stretching, etc but I’m just not sure where to start. A particular drug is easy to research, but exercise regimes vary so much it is difficult to provide a focused story. If anyone has any ideas, we’d love to hear them.
    I am only aware of one clinical trial currently ongoing for PD and attention deficit. It is being conducted by the University of Chicago and it will look at taking a “multidisciplinary approach to manage gait difficulty” in people with Parkinson’s disease. It appears to be focused on combinations of drugs that will hopefully help improve attention as well, but may also have a behavioural component. It could be worth investigating if interested (Click here to read more: https://clinicaltrials.gov/ct2/show/NCT02857244?).
    In addition, I have found several other clinical trial results recently regarding ADHD and PD. Most notably (https://www.ncbi.nlm.nih.gov/pubmed/21464430?dopt=Abstract ; the article is available on OPEN ACCESS here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3068005/ ; for details regarding the trial click here: https://clinicaltrials.gov/ct2/show/NCT00526630? ). The investigators were looking at whether methylphenidate could improve gait impairment in PD. It did not. And unfortunately it tended to worsen measures of motor function, sleepiness, and quality of life (and this was a double blind study). So perhaps this treatment should be avoided in folks who think they have a combination of ADHD and PD. I will keep an eye out for any planned clinical trials for PD and ADHD.
    I hope all of this helps.
    Kind regards,
    Simon

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